CASH AND CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS; BANK OVERDRAFT (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended									3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended	3 Months Ended	12 Months Ended
	Oct. 31, 2011	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010	Mar. 31, 2012 Ruble-denominated deposits	Dec. 31, 2011 Ruble-denominated deposits	Mar. 31, 2012 US dollar-denominated deposits	Dec. 31, 2011 US dollar-denominated deposits	Mar. 31, 2012 Low end of range D	Mar. 31, 2012 Low end of range Ruble-denominated deposits	Dec. 31, 2011 Low end of range Ruble-denominated deposits	Mar. 31, 2012 Low end of range US dollar-denominated deposits	Dec. 31, 2011 Low end of range US dollar-denominated deposits	Mar. 31, 2012 High end of range D	Mar. 31, 2012 High end of range Ruble-denominated deposits	Dec. 31, 2011 High end of range Ruble-denominated deposits	Mar. 31, 2012 High end of range US dollar-denominated deposits	Dec. 31, 2011 High end of range US dollar-denominated deposits
CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS
Deposits in banks with original maturity period for classification as short-term investments (in days)										91					365
Bank accounts						$ 10,916	$ 6,434	$ 18,316	$ 4,479
Other		1,425	1,418
Cash and cash equivalents (Note 4)		30,657	12,331	81,547	59,565
Short-term investments		98,815	117,233			87,867	102,068	10,948	15,165
Annual interest rate (as a percent)											5.00%	4.10%	0.90%	2.10%		8.70%	8.70%	2.60%	2.20%
Annual interest (as a percent)	7.20%
Credit limit under overdraft agreement	34,000
Overdraft position		$ 18,457	$ 16,941